Research And Implementation Of High Frame Rate Imaging Algorithm For Underwater Sonar Based On Coded Excitation

Underwater imaging sonar technology has been widely used in the exploration of submarine topography and inland lakes and rivers for a long time.However,the frame rate of the underwater imaging system is difficult to improve because the underwater imaging system needs to transmit and receive ultrasonic signals for many times.With the development of MIMO technology and high power electronic devices,ultrasonic coded signal has been applied in underwater acoustic detection.In this dissertation,a high frame rate imaging method based on orthogonal coding excitation is designed,aiming at the system transmitting signal and its corresponding high frame rate imaging method.The imaging method has the characteristics of high imaging frame rate and good anti-interference performance,which can effectively improve the imaging frame rate of underwater detection system.Finally,the corresponding hardware coding transmission circuit is designed to verify the feasibility of the coding signal.The research contents include:1.An array beamforming algorithm based on coded signal excitation is proposed.Through the introduction of conventional beamformer,the adaptive beamforming imaging algorithm based on coded modulation designed in this chapter is introduced.The method uses virtual array technology,uses coded signal as transmit signal,and uses minimum mean square error(LMS)beamformer for imaging calculation.The simulation results show that the coded excitation imaging method can effectively use the bandwidth and orthogonality of the coded signal to improve the imaging resolution and image contrast.At the same time,it only needs one time to transmit and receive,which improves the single imaging frame rate.2.A high frame rate imaging algorithm based on balanced gold LFM orthogonal coding excitation is proposed.In this algorithm,the autocorrelation and cross-correlation characteristics of balanced gold symbols and the high pulse compression ratio of LFM signal are used to realize the high frame rate imaging algorithm of underwater sonar two-dimensional array.Through the design of simulation experiments,it is verified that this imaging method has high imaging rate and imaging signal-to-noise ratio.And it is verified that when the echoes generated by the orthogonal coded excitation signals are overlapped in space,the imaging method can also perform the corresponding imaging operation for each orthogonal signal,reduce the artifacts,improve the image contrast,and improve the imaging frame rate of continuous imaging.3.A transmitting circuit of ultrasonic code is designed and made.In this circuit,FPGA chip controls DAC chip to generate corresponding coded signal waveform through digital interface,and adopts direct digital frequency synthesis technology to make the system flexibly adjust the coding form and length.The output signal waveform of DAC chip generates the corresponding PWM waveform through the PWM modulation circuit.The PWM waveform is used to control the class D power amplifier to amplify the power of the waveform and realize the purpose of driving the ultrasonic transducer.Finally,the coding waveform of the oscilloscope is given to verify the effectiveness of the coding transmitting circuit.Research...